An LED Driver with Wide Operation Range for Automotive Lighting

A light-emitting diode (LED) driver for the automotive lamp is proposed. The power conversion circuit of the driver combines a step-down converter and a step-up converter to cope with the variation of the input voltage by interchanging the association active power switches and regulating the duty-ratios. The circuit operations for voltage step-up and step-down modes are analyzed, and then the circuit parameters are designed accordingly. A laboratory circuit is designed for a motorcycle headlamp with five LEDs in series, which is powered by a dc source with wide input and output voltage ranges. Experimental results have demonstrated that the LEDs driver can be swapped between the step-up mode and step-down mode and adjust the lamp current properly for an input voltage range from 8 V to 13.5 V with the two to five LEDs in operation. A high efficiency can be achieved in the case that the difference between the input voltage and the output voltage is small. The highest efficiency can be as high as 98.2 %.